Abstract
Nanoscale studies of bone provide key indicators to evidence subtle structural changes that may occur in the biomedical, forensic and archaeological contexts. One specific problem encountered in all those disciplines, for which the identification of nanostructural cues could prove useful, is to properly monitor the effect of heating on bone tissue. In particular, the mechanisms at work at the onset of heating are still relatively unclear. Using a multiscale approach combining Raman microspectroscopy, transmission electron microscopy (TEM), synchrotron quantitative scanning small-angle X-ray scattering imaging (qsSAXSI) and polarized light (PL) microscopy, we investigate the ultrastructure of cortical bovine bone heated at temperatures < 300°C, from the molecular to the macroscopic scale. We show that, despite limited changes in crystal structure, the mineral nanoparticles increase in thickness and become strongly disorganized upon heating. Furthermore, while the nanostructure in distinct anatomical quadrants appears to be statistically different, our results demonstrate this stems from the tissue histology, i.e. from the high degree of heterogeneity of the microstructure induced by the complex cellular processes involved in bone tissue formation. From this study, we conclude that the analysis of bone samples based on the structure and organization of the mineral nanocrystals requires performing measurements at the histological level, which is an advantageous feature of qsSAXSI. This is a critical aspect that extends to a much broader range of questions relating to nanoscale investigations of bone, which could also be extended to other classes of nanostructured heterogeneous materials.
Highlights
Identifying the precise impact of heating on bone constitutes a challenge for archaeological and forensic sciences [1,2,3]
Using a multiscale approach combining Raman microspectroscopy, transmission electron microscopy (TEM), synchrotron quantitative scanning small-angle X-ray scattering imaging and polarized light (PL) microscopy, we investigate the ultrastructure of cortical bovine bone heated at temperatures < 300 ̊C, from the molecular to the macroscopic scale
Micro-thermal, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and Fourier transformed infrared (FTIR) spectroscopy investigations have, shown that the organic matrix undergoes a series of structural modifications before degradation at ~ 400 ̊C [6,15,16,17,18]
Summary
Identifying the precise impact of heating on bone constitutes a challenge for archaeological and forensic sciences [1,2,3]. Micro-thermal, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and Fourier transformed infrared (FTIR) spectroscopy investigations have, shown that the organic matrix undergoes a series of structural modifications before degradation at ~ 400 ̊C [6,15,16,17,18] Such changes are well correlated with macroscopic weight loss, volume shrinkage and decrease in hardness [19]. Many studies undertaken with X-ray diffraction (XRD) conclude that the mineral nanocrystals size and structure are not modified before ~ 400–600 ̊C, above which coalescence and recrystallization phenomena occur [19,20,21] Such effects were confirmed by scanning electron microscopy (SEM) [22] and were used to estimate the heating temperature in archaeological contexts [21,23,24]. Several authors have pointed to the presence of a hydrated layer at the surface of the mineral nanocrystals [27,28] which should be strongly affected by heat
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